1. Field of the Invention
This invention relates to a failure determination apparatus and method and an engine control unit for determining the failure of a temperature sensor that detects a temperature which changes according to an operating condition of an internal combustion engine.
2. Description of the Prior Art
Conventionally, a failure determination apparatus for a temperature sensor of the above-mentioned kind was proposed e.g. by Japanese Patent Publication (Kokoku) No. 3-56417. The failure determination apparatus determines the failure of a temperature sensor comprised of a thermistor, such as an intake air temperature sensor or an engine coolant temperature sensor, assuming that the output value of the temperature sensor decreases with an increase in temperature. The failure determination apparatus includes a control circuit connected to the temperature sensor, and the control circuit determines the failure of the temperature sensor based on the output value of the temperature sensor in the following manner: First, it is determined whether or not a first predetermined time period (e.g. 10 minutes) has elapsed after a start of an internal combustion engine. This is for allowing the engine to be warmed up to raise a temperature to be detected by the temperature sensor, thereby reducing the actual output value of the temperature sensor to a sufficiently reduced value. Then, when the first predetermined time period has elapsed after the start of the engine, the output value of the temperature sensor is compared with a predetermined reference value, and when a state of the output value of the temperature sensor being larger than the reference value has continued for a second predetermined time period or longer, it is determined that the temperature sensor is faulty. In short, according to the proposed failure determination apparatus, the temperature sensor is not determined to be faulty immediately after the temperature sensor has temporarily output a value exceeding the reference value, but only after the temperature sensor has continued to output larger values than the reference value over the second predetermined time period, it is determined that the temperature sensor is faulty since the output therefrom is fixed. The above determining process enables the failure determination apparatus to avoid erroneous determination of the failure of the temperature sensor which might be caused by a temporary error in output from the temperature sensor itself, or noises.
The above failure determination apparatus, however, takes a long time (first predetermined time period+second predetermined time period) from the start of the engine before it finally determines that the temperature sensor is faulty. For this reason, e.g. in determining the amount of fuel to be supplied to the engine at the start thereof depending on the temperature detected by the above temperature sensor, if the temperature sensor is faulty, the output from the temperature sensor can indicate a high temperature to be detected after completion of warming-up of the engine even during a cold start of the same. In this case, since the amount of fuel to be supplied to the engine is determined depending on the output from the faulty temperature sensor, the operation of the engine after the start becomes unstable due to insufficient supply of fuel, and it takes a long time before the engine is fully warmed up.
Further, in the above failure determination apparatus, the start of comparison between the output value of the temperature sensor and the reference value is determined only by reference to time elapsed after the start of the engine. This can bring about the following problems: When the engine is started in an extremely cold condition, or when idling operation continues thereafter, the engine is not sufficiently warmed up even after the lapse of the first predetermined time period from the engine start, so that the output value of the temperature sensor may not become lower than the reference value. In this case, if the state continues over the second predetermined time period, the temperature sensor is erroneously determined to be faulty even though it is not faulty, i.e. normally functioning.
It is an object of the invention to provide a failure determination apparatus and method and an engine control unit which are capable of determining the failure of a temperature sensor promptly and correctly, regardless of environmental conditions at the start of an internal combustion engine using the temperature sensor.
To attain the above object, according to a first aspect of the invention, there is provided a failure determination apparatus and method an engine control unit for determining failure of a temperature sensor that detects a temperature which changes according to an operating condition of an internal combustion engine.
The failure determination apparatus according to the first aspect of the invention is characterized by comprising:
operation progress parameter calculation means for calculating an operation progress parameter indicative of a degree of progress of operation of the engine after the engine has started;
temperature memory means for storing a value of the temperature detected by the temperature sensor when the engine is stopped;
stop time measurement means for measuring a stop time period from a stoppage to a start of the engine; and
failure determination means for determining that the temperature sensor is faulty, when a difference between a value of the temperature detected by the temperature sensor at the start of the present operation of the engine and the value of the temperature stored in the temperature memory means is equal to or smaller than a predetermined reference value, on condition that the operation progress parameter calculated during an immediately preceding operation of the engine is larger than a predetermined value, and that the stop time period before the start of the present operation of the engine is longer than a predetermined time period.
According to this failure determination apparatus, when the internal combustion engine is started, a temperature which changes according to the operating condition of the engine is detected by the temperature sensor, and the operation progress parameter indicative of the degree of progress of the operation of the engine from the start thereof is calculated by the operation progress parameter calculation means. Then, when the operation of the engine is stopped, a value of the temperature detected at a stoppage of the engine is stored by the temperature memory means. Further, a stop time period from a time point of the stoppage of engine to a time point the engine is started again is measured by the stop time measurement means. As a result, when the difference between the value of the temperature detected by the temperature sensor at the start of the present operation of the engine and the value of the temperature stored in the temperature memory means is equal to or smaller than the predetermined reference value on condition that the operation progress parameter calculated during the immediately preceding operation of the engine is larger than the predetermined value, and that the stop time period before the present operation of the engine is longer than the predetermined time period, it is determined that the temperature sensor is faulty. In other words, if the temperature sensor is normal, a value of the temperature output from the temperature sensor at a stoppage of the engine after a full operation thereof should be sufficiently high, and further if a long stop time period has elapsed after the immediately preceding operation of the engine, a value of the temperature output from the temperature sensor at the start of the present operation should be sufficiently lower than the value of the temperature detected at the stoppage of the immediately preceding operation of the engine, which means the difference between the two temperature values is large. Therefore, since the difference between the two values of the temperature should be normally large, by determining that the temperature sensor is faulty if the difference is equal to or smaller than the predetermined reference value, it is possible to determine the failure of the temperature sensor correctly, regardless of environmental conditions at the start of the engine. Further, since the determination of failure of the temperature sensor can be carried out at the start of the present operation, the failure determination apparatus according to the first aspect of the present invention is capable of determining the failure of the temperature sensor promptly at the start of the engine, differently from the prior art.
To attain the above object, according to a second aspect of the invention, there is provided a failure determination apparatus for determining failure of a temperature sensor that detects a temperature which changes according to an operating condition of an internal combustion engine.
The failure determination apparatus according to the second aspect of the invention is characterized by comprising:
an operation progress parameter calculation module for calculating an operation progress parameter indicative of a degree of progress of operation of the engine after the engine has started;
a temperature memory module for storing a value of the temperature detected by the temperature sensor when the engine is stopped;
a stop time measurement module for measuring a stop time period from a stoppage to a start of the engine; and
a failure determination module for determining that the temperature sensor is faulty, when a difference between a value of the temperature detected by the temperature sensor at the start of the present operation of the engine and the value of the temperature stored by the temperature memory module is equal to or smaller than a predetermined reference value, on condition that the operation progress parameter calculated during an immediately preceding operation of the engine is larger than a predetermined value, and that the stop time period before the start of the present operation of the engine is longer than a predetermined time period.
This failure determination apparatus according to the second aspect of the invention provides the same advantageous effects as described above concerning the failure determination apparatus according to the first aspect of the invention.
To attain the above object, according to a third aspect of the invention, there is provided a failure determination method of determining failure of a temperature sensor that detects a temperature which changes according to an operating condition of an internal combustion engine.
The failure determination method according to the third aspect of the invention is characterized by comprising the steps of:
calculating an operation progress parameter indicative of a degree of progress of operation of the engine after the engine has started;
storing a value of the temperature detected by the temperature sensor when the engine is stopped;
measuring a stop time period from a stoppage to a start of the engine; and
determining that the temperature sensor is faulty, when a difference between a value of the temperature detected by the temperature sensor at the start of the present operation of the engine and the stored value of the temperature is equal to or smaller than a predetermined reference value, on condition that the operation progress parameter calculated during an immediately preceding operation of the engine is larger than a predetermined value, and that the stop time period before the start of the present operation of the engine is longer than a predetermined time period.
This failure determination method according to the third aspect of the invention provides the same advantageous effects as described above concerning the failure determination apparatus according to the first aspect of the invention.
To attain the above object, according to a fourth aspect of the invention, there is provided an engine control unit including a control program for causing a computer to determine failure of a temperature sensor that detects a temperature which changes according to an operating condition of an internal combustion engine.
The engine control unit according to the fourth aspect of the invention is characterized in that the control program causes the computer to calculate an operation progress parameter indicative of a degree of progress of operation of the engine after the engine has started, store a value of the temperature detected by the temperature sensor when the engine is stopped in a memory device of the computer, measure a stop time period from a stoppage to a start of the engine, and determine that the temperature sensor is faulty, when a difference between a value of the temperature detected by the temperature sensor at the start of the present operation of the engine and the value of the temperature stored in the memory device is equal to or smaller than a predetermined reference value, on condition that the operation progress parameter calculated during an immediately preceding operation of the engine is larger than a predetermined value, and that the stop time period before the start of the present operation of the engine is longer than a predetermined time period.
This engine control unit according to the fourth aspect of the invention provides the same advantageous effects as described above concerning the failure determination apparatus according to the first aspect of the invention.
In each aspect of the invention, it is preferable that the operation progress parameter is at least one of an integrated value of an operation time period over which the engine has been operated since the start thereof, an integrated value of a travel distance over which a vehicle on which the engine is installed has traveled since the start thereof, and an integrated value of an amount of fuel which has been supplied to the engine since the start thereof.
According to this preferred embodiment of each aspect of the invention, the temperature of the engine generally becomes higher as any of the integrated values of the operation time period, the travel distance, and the amount of fuel supply becomes larger. Therefore, whether or not the temperature of the engine is sufficiently high can be properly determined by using at least one of these integrated values as the operation progress parameter, and hence it is possible to determine the failure of the temperature sensor correctly.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.